Ki (気) is the Japanese (Romaji) version of Qi (or Ch'i); a term most oftenly used in our context to define the internal energy of man, animal, and nearly everything. From hereon, Ki also refers to Qi and Chi, since they are essentially the same, just different spellings of the same principle.
Although there are still some differences in the actual interpretation of what Ki actually is, practicioners have agreed on a few things. Since most traditional practicioners focus on it's use and application in the human body, this entry will relate to that point of view. Ki is the energy that flows inside everyone. A person's Ki was there when they were born, and it will be there when they die. Without Ki, it is said, there would be nothing; not even darkness.
The word Ki can be translated as "energy," but can also refer to air, flavor, senses, intuition, emotions, or willpower. In some modern usages, Ki is even used in an entirely physical sense to refer exclusively to the usage of leverage and body or joint positioning. Other uses blur the lines between Ki as a physical leverage or positioning and Ki as a metaphysical energy, allowing a synergy between the physical and the metaphysical energies being used.
We know that the concept originated from China, but there is very little known about the actual origins of the concept of Ki. One of the earliest and best documented references to Ki is in the well-known treatise on TCM, the Nèijing: Medical Canon of the Yellow Emperor - attributed to the Yellow Emperor Huang Di and written somewhere between 2700 and 2500 B.C. (although many historians do believe that the actual text was compiled much later). Ki itself, however, has been mentioned since the very first 'written' records of Chinese society, detailing breathing exercises.
In etymology; the (older) Kanji for Ki comes from a metaphor, namely 'steam rising from boiling water' - this in term referring to the transformation of boiling water; first it's completely still, but slowly a vapor arises from the water, only to eventually turn into a powerful force that bubbles from the water, to the top and into the atmosphere. The usage of the word Ki is quite widespread; a lot of things are indicated with Ki. "I have Ki for you", for instance, means that you really like the person. And of course, it is also a common term in martial arts; an example that is almost too easy would be Aikido, an art that relies heavily on the coordination and training of one's Ki.
Chuen, Master Lam Ken, (1999. 2nd print, 2002) The Way of Healing. Gaia Books, London.
Khor, Gary (2004) Reflections on Qi. New Holland Publishers, Sydney. ISBN 1-84330-795-2
Westbrook, A and Ratti, O (47th print, 1998) Aikido and the Dynamic Circle. Charles E. Tuttle comp., Japan.